Rate: Can occur at any rateRegularity: Regular but interruptedP wave: Normal before pause; may be different or absent afterPR interval: Normal before pause; may be different or absent afterQRS interval: < 0.12 unless ventricular escape beat presentCause: Sinus node ischemia, hypoxia, digitalis toxicity, excessive vagal tone, medication side effectsAdverse Effects: Maybe none; maybe decreased cardiac output; lower pacemaker may take over after pauseTreatment: Consider O2; atropine or pacemaker if symptoms

Sinus Exit Block

Rate: Can occur at any rateRegularity: Regular but interruptedP wave: Normal before and after the pause; all shaped the samePR interval: 0.12 - 20QRS interval: < 0.12Cause: Medication side effects, excessive vagal tone, hypoxiaAdverse Effects: Same as sinus arrest; pause is a multiple of R-R; sinus resumes after pauseTreatment: Consider O2; atropine or pacemaker if symptoms

Rate: Can occur at any rateRegularity: Regular but interruptedP wave: Inverted before or after QRS or hidden inside QRSQRS interval: < 0.12Cause: Stimulants, caffeine, hypoxia, heart disease, or normalAdverse Effects: Usually no ill effectsTreatment: Usually none required

Rate: Can occur at any rateRegularity: Regular but interruptedP wave: Usually noneQRS interval: > 0.12; wide and bizarre in shapeCause: Hypoxia, MI, hypokalemia, low magnesium, caffeine, stimulants, stressAdverse Effects: Occasional are no problem; can lead to lethal arrhythmias if frequent or after an MITreatment: Amiodarone, O2, lidocaine, atropine for bradycardic PVCs

Rate: 40 - 100Regularity: Usually regular- can be irregular at timesP wave: Dissociated if even presentQRS interval: > 0.12; wide and bizarre in shapeCause: Most often seen during MIAdverse Effects: Usually well toleratedTreatment: Atropine, epinephrine, dopamine if HR low and symptoms

V-tach

Rate: 100 - 250Regularity: Usually regular - can be irregular at timesP wave: Dissociated if even presentQRS interval: > 0.12; wide and bizarre in shapeCause: Hypoxia, MI, hypokalemia, low magnesium, caffeine, stimulants, stressAdverse Effects: May be tolerated OK for short bursts; can cause shock, unconsciousness, and death if untreatedTreatment: Amiodarone, lidocaine, O2, cardioversion or defib, CPR if no pulse

Rate: Atria: 60-100; Ventricle: less than atrial rateRegularity: Regular but interrupted or irregular; groups of beats, then a pauseP wave: Normal; one not followed by a QRS; all shaped the samePR interval: Gradually prolongs until a QRS is droppedQRS interval: QRS < 0.12Cause: MI, digitalis toxicity, medication side effectsAdverse Effects: Usually well tolerated, but watch for worsening AV blockTreatment: Pacemaker, atropine, epinephrine or dopamine if symptoms from low HR